If she wants usdt she might be living in a place that needs the short term “stability” so in that case I’d use something like people mention, aqua or blink wallet. 

If she uses something like binance or kraken, they can receive and sell bitcoin to usdt right on the spot (I’ve a friend that lives in Venezuela and for stuff like this is what I do) but I use strike. It will also send fiat through lightning so I don’t have to bother with exchanges rates.